This invention relates to a lens grinding apparatus and lens grinding method for grinding a lens to conform it to the shape of an eyeglass frame, as well as components in connection with the apparatus and the method.
In a lens grinding apparatus for grinding an eyeglass lens to conform it to the shape of an eyeglass frame, a lens is worked on as it is chucked between two lens rotating shafts. To chuck the lens, a fixing (securing) cup is first set on the front surface of the lens in the desired position determined with a centering device. The base of the fixing (securing) cup is fitted in a cup receptacle mounted on one of the two lens rotating shafts and the lens is chucked with its rear surface being held in position with a lens retainer mounted on the other lens rotating shaft.
The lens being ground is under the stress of the reaction and rotating forces provided by the lens grinding wheel. If the chucking force is smaller than the stress, the axial misalignment of the lens may occur. To avoid this problem and secure the necessary chucking force, a lens having a sufficient diameter to work on is ground using a circular fixing (securing) cup with a large diameter across the mounting surface and a circular lens retainer also having a large diameter.
However, if a lens for "granny's glasses" which has a small distance between the upper and lower edges is processed using a fixing (securing) cup, a cup receptacle and a lens retainer which are of the same sizes as in the case of processing lenses having a sufficient diameter to work on, these components will interfere with the lens grinding wheel. To avoid this problem, they must be replaced by components of smaller diameters which are specially intended for use in the processing of lenses for "granny's glasses".
However, replacing the cup receptacle and the lens retainer according to the lens diameter to be worked on is not only more time-consuming than one will usually expect but also cumbersome. Frequent replacing operations will reduce the efficiency of the lens processing operation at a processing center where a large number of lenses are collectively worked at the request of optician's shops.